1. Field of the Invention
The present invention relates to a sensor system in which a plurality of sensor bodies of a number of head separation type sensors (for example, fiber type photoelectric sensors, ultrasonic sensors, proximity sensors and the like) are arranged aligned with each other by means of a DIN (Deutsche Institute Normenausschuss) rail or the like.
2. Description of the Background Art
In the technical field of FA (Factory Automation), for example, head separation type sensors (for example, fiber type photoelectric sensors, ultrasonic sensors, proximity sensors and the like) are widely used to detect presence/absence and positions of objects. When a fiber type photoelectric sensor is used, for example, a sensor head for emitting and receiving a detection beam (red light beam, infrared ray or the like) is placed in a narrow space near an object of detection, while a sensor body containing a light emitting element and a light receiving element is accommodated in a control panel placed away from the object of detection, with the sensor head and a sensor body coupled by an optical fiber. Generally, the outer shape of the sensor body casing is a thin rectangular cube. When a number of sensor bodies are to be accommodated in the control panel, the bodies are typically arranged in contact with each other to form a row, using the DIN rail.
FIG. 17 schematically shows an example of a sensor system in which sensor bodies of fiber type photoelectric sensors (hereinafter simply referred to as “sensor bodies”) are arranged in contact with each other to form a row. As can be seen from FIG. 17, a plurality of sensor bodies 402 for detecting different objects are arranged in a row in the transverse direction on a DIN rail 401 mounted in the control panel. From a front surface of each of the sensor bodies 402, optical fibers 403 and 404 constituting outgoing and returning paths for the detection beam, respectively, are drawn out, and from the rear end surface of the case, an electric cord 405 including a power feed line 405a and a signal line 405b (see FIG. 18) is drawn out.
When a detection beam path 408 is opened for transmission or intercepted between sensor head portions 403a and 404a at the tip ends of optical fibers 403 and 404, internal circuitry of the sensor body functions, and a detection signal (a switching signal or an analog signal corresponding to the amount of received light) is externally output through the signal line 405b in the electric cord 405. The detection signal is supplied as a control input, to a programmable logic controller (PLC) 407, as shown in FIG. 18.
Further, as shown in FIG. 18, power supply from a power source 406 to each of the sensor bodies 402 is effected through the power feed line 405a. Power feed line 405a includes two, that is, positive and negative, lines.
In this manner, in the conventional photoelectric sensor systems in which a number of sensor bodies 402 are arranged aligned with each other and in contact with each other, it is necessary to supply power to each of the photoelectric sensor bodies 402 through power feed line 405a in the electric cord. Therefore, for the electric cord, a cord having a large number of core lines is necessary, and, in addition, it takes time and labor just to connect these lines.
A structure saving lines in this type of photoelectric sensor system has been known, as described in Japanese Patent Laying-Open No. 9-64712. According to the technique described in this Laid-Open Application, the sensor system includes one main sensor (body) and a plurality of sub sensors (bodies) arranged in a row and in contact with the main sensor and with each other. An electric cord including both the signal line and the power feed line is main sensor, and an electric cord including the signal line only is connected to each sub sensor, by joining means that will fix the position such as solder. On the side surfaces of the cases of the main and sub sensors, there are a male junction and female junction to provide interface between neighboring sensors. When the main sensor is connected to a sub sensor and the neighboring sub sensors are connected to each other by connected to the these joints, the power supplied to the main sensor through the electric cord is successively passed through a conductor in each sensor case, to the series of sub sensors.
In the sensor system described in Japanese Patent Laying-Open No. 9-64712, feeding and receiving of power through the conductors in the sensor cases through the male and female joints connecting the neighboring sensor bodies with each other is possible, whereby the reduction of lines can be achieved, as power supply to individual sub sensor through the electric cord is made unnecessary.
In such a sensor system, however, two different sensor bodies, that is, one having such a structure that receives external power through the electric cord, and one having such a structure that receives power through the male and female joints from the neighboring sensor body are necessary. This means that the number of parts and the steps of parts management increase, resulting in increased cost. Further, inventory management of the sensor bodies is troublesome, as there are two different types of the sensor bodies.
Further, when trouble occurs in any of the sensors (main or sub), it becomes necessary to change the electric cord connected to the defective sensor at the same time. This requires time consuming and troublesome work of disconnecting the bundle of electric cords and newly connecting substitute electric cords, and material waste increases.